1. Field of the Invention
The present invention relates to a method of testing a printed circuit board not yet mounted electrical circuit elements or a printed circuit board already mounted circuit elements as to whether there are defective circuit breaks; whether there are required integrated circuits, resistors, capacitors or other electrical circuit elements in position; and whether these circuit elements function well, and to a printed circuit board tester using such method.
2. Description of Related Art
The printed circuit board testing method and apparatus required the selection and use of jigs exclusively designed for different printed circuit boards to test and make a decision as to which printed circuit boards should be passed or rejected. Recently an improved tester has been proposed in which measuring probes are moved laterally and longitudinally on one of the opposite major surfaces of a printed circuit board to be tested under the control of a microcomputer, thereby permitting the measuring probes to be in contact with selected measuring points one after another according to a measuring program (U.S. Pat. No. 5,107,206). This tester can be used advantageously in testing different printed circuit boards without requiring jigs.
In use a printed circuit board is fixed in position in the tester, and then a plurality of measuring probes are put selected measuring points to provide electric signals. These electric signals are measured and processed with the aid of meters and microcomputers to make a decision as to the printed circuit board should be rejected or passed.
In fixing a selected printed circuit board in position the reference apertures of the printed circuit board are put in registration with the reference pins of a printed circuit board setting frame, and then the printed circuit board thus put in correct position are gripped and fixed by its opposite edges. Another tester uses a matrix of measuring probes on which one major surface of a selected printed circuit board is put by applying a negative pressure thereto for testing.
In these conventional printed circuit board testers a printed circuit board to be tested is fixed simply by gripping its opposite edges, and the printed board cannot be unbent if it is bent.
The bending of the printed circuit board is likely to increase with the increase of the printed circuit board size. With such bending of the printed circuit board and with the increased density of circuit elements per unit area in the printed circuit board (and accordingly caused undesired deviations of selected measuring points), the measuring probe cannot come to touch selected measuring points. In fact, the measuring probe often fails to hit exactly the right point but come close to it, or hit a wrong point adjacent to the right one.
As for the method of applying one major surface of a selected printed circuit board to a matrix of measuring probes under negative pressure, the printed circuit board can be unbent to a straight posture, but disadvantageously the simultaneous testing of the opposite major surfaces of the printed circuit board is not permitted, accordingly lowering the measuring efficiency. Still disadvantageously, the negative pressure applying unit is rather bulky and complex in structure, accordingly the manufacturing cost increases.
As a recent tendency printed circuit boards are equipped with parts and elements at an ever increasing density, and the conventional method cannot be used in testing such high-density printed circuit boards.